The higher olefins oligomerization process converts light olefins, typically, C3 to C6 light olefins, to oligomers (higher olefins), typically such as octenes, nonenes and dodecenes. These higher olefins are then used in the production of various products such as plasticizers and solvents. The feedstocks used for the higher olefins oligomerization process come from various sources, such as catalytic crackers and steam crackers. Such feeds are known to contain nitrogen containing compounds, which act as poisons for the catalysts typically used in the higher olefins oligomerization process. The presence of poisons in the feeds has a significant impact on the catalyst life, and thus on the operation and economics of the higher olefins oligomerization process. It is known that acidic catalysts like solid phosphoric acid or zeolites typically used in olefin oligomerization processes are susceptible to poisoning from trace amounts of sulphur-, nitrogen- and oxygen-containing compounds in the feed. Such poisons adsorb on the acidic catalysts, blocking acid sites and pores. This causes enhanced deactivation of the catalyst and shorter catalyst life. Special precautions and feed cleanup is required in case the poison levels are too high.
At present there is no known single process that can quantitatively remove all nitrogen poisons from olefin feeds useful in the higher olefins oligomerization process to meet required feed quality specifications. Water washing only partially removes nitriles, such as acetonitrile, from certain olefin feeds. Not only is the removal process difficult but it is expensive and generates a lot of waste water.
The interaction of acetonitrile with olefins and alcohols in zeolite H-ZSM-5 is described in Chem. Eur. J. 1997, 3, No. 1 pages 47 to 56 “Interaction of Acetonitrile with Olefins and Alcohols in Zeolite H-ZSM-5: In-Situ Solid-State NMR Characterization of the Reaction Products” Alexander G. Stepanov and Mikhail v. Luzgin.
U.S. Pat. No. 4,973,790 discloses a process for oligomerizing C2 to C10 olefins obtained by catalytic cracking of heavy crude oil. Feed pretreatment is practised to remove basic nitrogen compounds present in the light olefin feed with a water wash or guard bed. Where the pretreatment comprises at least two steps, the first step is either a water wash step or contact of feed with a solid bed having an affinity for basic nitrogen. The second step is contact with a zeolitic bed. Only use of a conventional resin guard bed is exemplified. No specific nitrogen compounds are mentioned.
U.S. Pat. No. 5,414,183 discloses isomerization and etherification reactions. Nitrogen contaminants in the hydrocarbon feed stream are converted to hydrolysis products by contact with an alkaline solution. Residual products in the hydrocarbon phase may be removed by a variety of known means including water washing, stripping and adsorption.
US 2005/0137442 relates to a transalkylation process where organic nitrogen compounds, including acetonitrile and propionitrile, are removed from an aromatic feed stream by contacting the stream with an acidic molecular sieve at a temperature of at least 120° C.
US2007/0086933 discloses a translakylation process for reacting carbon number nine aromatics with toluene to form carbon number eight aromatics such a para-xylene. The process uses a guard bed of gamma aluminium oxide made from boehmite crystals, prior to contacting with a translakylation catalyst in order to remove chlorides from the aromatic feed.
WO2004/014546 teaches a guard bed made of finely divided lead oxide and a particulate support material, such as aluminium oxide. This guard bed can be used to remove chlorides present in a process gas stream containing carbon monoxide and steam, before contact with a copper containing catalyst.